1. Field of the Invention
The present invention relates to a steplessly height-adjustable armrest, more particularly one, which is structured in such a manner as not to move to a lower position accidentally when it is pressed.
2. Brief Description of the Prior Art
It is a major concern of chair manufacturers to provide more comfortable chairs to the consumers. The seats and backs of currently existing chairs are usually formed with a certain curvature according to ergonomics. And, certain kinds of chairs are equipped with armrests for sitters to comfortably rest their arms on, which are best adjustable in height to be suitable for different persons.
Referring to FIGS. 6 and 7, a currently existing height adjustable armrest 5 consists of a base 51, a fixed tube 52, and an armrest main part 54. The base 51 is securely joined to a seat, and the fixed tube 52 is securely joined to the base 51. A rack 53 is secured in the fixed tube 52. The armrest main part 54 is inserted in the fixed tube 52 in a movable manner, and an ornamental cover 55 is positioned around and joined to the armrest main part 54, and covers the fixed tube 52. The armrest main part 54 has a step-shaped portion 541. The cover 55 has a hole 551. A gear 56 is fitted on the main part 54 to engage the rack 52, and an immobilizing member 57 is arranged right above the gear 56, and up and down displaceable relative to the armrest main part 54. The immobilizing member 57 has a lower toothed portion 571, an upper rod part 572, and a step-shaped portion 573 adjoining the upper rod part 572. An elastic element 58 is positioned around the rod part 572 of the immobilizing member 57, and contacts the step-shaped portions 541 and 573 at upper and lower ends thereof respectively. An operating part 59 is securely joined to an upper end of the rod part 572 of the immobilizing member 57, and sticks out through the hole 551 of the ornamental cover 55. Therefore, the immobilizing member 57 is normally biased to a lower position to engage and immobilize the gear 56 by means of the elastic element 58, thus preventing the armrest main part 54 from moving accidentally.
When the user moves the operating part 59 so as to lift the immobilizing member 57, the immobilizing member 57 will disengage the gear 56; thus, the gear is free to rotate. Therefore, the armrest main part 54 can be moved to a new height with the gear 56 rolling on the rack 53 secured in the fixed tube 52. After the armrest 5 has been adjusted to a proper height, and the user released the operating part 59, the immobilizing member 57 will be biased back to the lower position to engage the gear 56 by the elastic element 58; thus, the armrest main part 54 is fixed in position.
The above adjustable armrest is found to have a drawback: because the immobilizing member is kept in the lower position to engage the gear by means of the elastic element, the immobilizing member and the gear can get out of engagement easily if the sitter stands up with his/her hands pressing the armrest main part. Consequently, the armrest main part will be moved down accidentally, and the sitter can get hurt. Therefore, such an armrest is neither safe nor convenient to use.
Therefore, it is a main object of the present invention to provide an improvement on a steplessly height-adjustable armrest structure to overcome the above problem.